Multi-quantum well structure and led device including the same

ABSTRACT

Disclosed is a multi-quantum well structure including a stress relief layer, an electron-collecting layer disposed on the stress relief layer, and an active layer including a first active layer unit that is disposed on the electron-collecting layer. The first active layer unit includes potential barrier sub-layers and potential well sub-lavers being alternately stacked, in which at least one of the potential barrier sub-layers has a GaN/Alx1Iny1Ga(1-x1-y1)N stack, where 0&lt;x1≤1 and 0≤y1&lt;1. An LED device including the multi-quantum well structure is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part (CIP) application of U.S.patent application Ser. No. 16/655832, filed on Oct. 17, 2019, which isa bypass CIP of International Application No. PCT/CN2018/078655,entitled “MULTI-QUANTUM WELL STRUCTURE AND LIGHT-EMITTING DIODETHEREOF,” filed on Mar. 12, 2018, which claims priority of ChineseInvention Patent Application No. 201710252090.7, filed on Apr. 18, 2017.

FIELD

This disclosure relates to a multi-quantum well structure, and an LEDdevice including the multi-quantum well structure.

BACKGROUND

As the light-emitting diode (LED) industry gradually develops, anincreasing need for developing white LED devices with high luminance anda tolerance toward high current density is observed. Meanwhile,miniaturization of the LED devices under the premise of maintainingtheir properties (especially luminance) is highly desirable in order toincrease the market competitiveness of the LED devices. This trendfurther elevates the need for tolerance toward high current density inan epitaxial structure of the LED devices, with the efficiency droopeffect remaining as one of the biggest problems to be solved.

Conventional epitaxial designs for increasing the tolerance toward highcurrent density and for reducing the efficiency droop effect in an LEDdevice are usually implemented by modifying the structure andcomposition of an electron-blocking layer disposed on an active layer.Such conventional epitaxial designs may include, for example, graduallychanging an Al content in an AlGaN electron-blocking layer, or formingthe electron-blocking layer with a superlattice structure such as anAlGaN/GaN superlattice structure, an AlN/GaN superlattice structure, andan AlN/AlGaN superlattice structure. However, such epitaxial designs maynot alleviate the energy-band distortion in the active layer of the LEDdevice. Further, a modification in structure and composition mayincrease the thickness of the electron-blocking layer, which results ina loss of light-emitting efficiency. In addition, a thickelectron-blocking layer with a relatively high Al composition mayfurther enlarge openings of V-pit defects in the LED device, whichresults in a thicker P-type cladding layer being needed to fill andflatten an epitaxial layer of the LED device in order to preventelectrostatic discharge and a loss of infrared functionalities.

SUMMARY

Therefore, a first object of the disclosure is to provide amulti-quantum well structure that can alleviate or eliminate at leastone of the drawbacks of the prior art. A second object of the disclosureis to provide a light-emitting diode (LED) device including themulti-quantum well structure. According to a first aspect of thedisclosure, a multi-quantum well structure includes a stress relieflayer, an electron-collecting layer disposed on the stress relief layer,and an active layer including a first active layer unit that is disposedon the electron-collecting layer. The first active layer unit includes aplurality of potential barrier sub-layers and a plurality of potentialwell sub-layers being alternately stacked. At least one of the potentialbarrier sub-layers of the first active layer unit has aGaN/Al_(x1)In_(y1)Ga_((1-x1-y1))N stack, where 0<x1≤1 and 0<y1≤1. Theone of the potential barrier sub-layers having theGaN/Al_(x1)In_(y1)Ga_((1-x1-y1))N stack is disposed farthest away fromthe electron-collecting layer. The one of the potential barriersub-layers of the first active layer unit farthest away from theelectron-collecting layer is undoped, and for the remainder of thepotential barrier sub-layers of the first active layer unit, each of thepotential barrier sub-layers is one of a n-doped layer and a p-dopedlayer.

According to a second aspect of the disclosure, an LED device includes asubstrate, a buffer layer disposed on the substrate, an N-type claddinglayer disposed on the buffer layer, the multi-quantum well structure ofthe first aspect of the disclosure which is disposed on the N-typecladding layer, a P-type cladding layer disposed on the multi-quantumwell structure, and a P-type contact layer disposed on the P-typecladding layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the disclosure will become apparent inthe following detailed description of the embodiments with reference tothe accompanying drawings, in which:

FIG. 1 is a schematic view of a first embodiment of a multi-quantum wellstructure according to the disclosure;

FIG. 2 is a schematic view of a first embodiment of a light-emittingdiode (LED) device according to the disclosure;

FIG. 3 is a schematic view of a second embodiment of the multi-quantumwell structure according to the disclosure;

FIG. 4 is a schematic view of a second embodiment of the LED deviceaccording to the disclosure;

FIG. 5 is a schematic view of a third embodiment of the multi-quantumwell structure according to the disclosure; and

FIG. 6 is a schematic view of a third embodiment of the LED deviceaccording to the disclosure.

DETAILED DESCRIPTION

Hereinafter, the embodiments will be described in detail with referenceto the accompanying drawings. It should be noted that the drawings,which are for illustrative purposes only, are not drawn to scale, andare not intended to represent the actual sizes or actual relative sizesof the components of the multi-quantum well structure and the LED deviceincluding the same. Moreover, where considered appropriate, referencenumerals have been repeated among the figures to indicate correspondingor analogous elements, which may optionally have similarcharacteristics.

First Embodiment

Referring to FIG. 1, a first embodiment of a multi-quantum wellstructure 100 according to the disclosure includes a stress relief layer110, an electron-collecting layer 120 disposed on the stress relieflayer 110, and an active layer 130. The active layer 130 includes afirst active layer unit 131 that is disposed on the electron-collectinglayer 120. The first active layer unit 131 of the active layer 130includes multiple pairs of sub-layers, the sub-layers in each pairincluding a potential barrier sub-layer and a potential well sub-layer.The plurality of potential barrier sub-layers and the plurality ofpotential well sub-layers of the first active layer unit 131 arealternately stacked. At least one of the potential barrier sub-layers ofthe first active layer unit 131 has a GaN/Al_(x1)In_(y1)Ga_((1-x1-y1))Nstack, where 0<x1≤1 and 0≤y1<1, and for the remainder of the potentialbarrier sub-layers of the first active layer unit 131, each of thepotential barrier sub-layers is a GaN layer. In this embodiment, each ofthe potential well sub-layers of the first active layer unit 131 is anInGaN layer.

In certain embodiments, in the GaN/Al_(x1)In_(y1)Ga_((1-x1-y1))N stack,y1=0 and 0.05≤x1≤1. That is, said at least one of the potential barriersub-layers of the first active layer unit 131 has theGaN/Al_(x1)Ga_((1-x1))N stack. In the GaN/Al_(x1)Ga_((1-x1))N stack(i.e., y1=0), the range of x1 may be 0.1≤x1≤1, 0.05≤x1≤0.20, or0.1≤x1≤0.15.

In certain embodiments, the one of the potential barrier sub-layershaving the GaN/Al_(x1)In_(y1)Ga_((1-x1-y1))N stack in the first activelayer unit 131 is disposed farthest away from the electron-collectinglayer 120.

In certain embodiments, in the first active layer unit 131, the one ofthe potential barrier sub-layers farthest away from theelectron-collecting layer 120 is undoped, and for the remainder of thepotential barrier sub-layers, each of the potential barrier sub-layersis one of an n-doped layer and a p-doped layer.

In certain embodiments, the one of the potential barrier sub-layers ofthe first active layer unit 131 farthest away from theelectron-collecting layer 120 has a thickness ranging from 140 Å to 190Å, and has the GaN/Al_(x1)Ga_((1-x1))N stack (i.e., y=0) with 0.05≤x1≤1.A thickness of Al_(x1)Ga_((1-x1))N in the GaN/Al_(x1)Ga_((1-x1))N stackranges from 20 Å to 30 Å.

In certain embodiments, the stress relief layer 110 includes less than30 pairs of sub-layers, the sub-layers in each pair including apotential barrier sub-layer and a potential well sub-layer. Theplurality of potential barrier sub-layers and the plurality of potentialwell sub-layers of the stress relief layer 110 are alternately stacked.Each of the potential barrier sub-layers is a GaN layer, and each of thepotential well sub-layers is an InGaN layer. An In amount in the stressrelief layer 110 is less than 15% based on a total weight of the stressrelief layer 110.

In certain embodiments, the stress relief layer 110 is an InGaN layer,where the In amount in the stress relief layer 110 is less than 15%based on a total weight of the stress relief layer 110.

The electron-collecting layer 120 includes multiple pairs of sub-layers,the sub-layers in each pair including a potential barrier sub-layer anda potential well sub-layer. The plurality of potential barriersub-layers and the plurality of potential well sub-layers of theelectron-collecting layer 120 are alternately stacked. In thisembodiment, the electron-collecting layer 120 includes three to sixpairs of the sub-layers. One of the potential barrier sub-layers of theelectron-collecting layer 120 (e.g., the one farthest away from thestress relief layer 110) has a GaN/Al_(x2)Ga_((1-x2))N/GaN stack, where0.05≤x2≤1, and for the remainder of the potential barrier sub-layers ofthe electron-collecting layer 120, each of the potential barriersub-layers is a GaN layer. In this embodiment, each of the potentialwell sub-layers of the electron-collecting layer 120 is an InGaN layerhaving an In concentration lower than that of the potential wellsub-layers of the first active layer unit 131. With the potentialbarrier sub-layer having the GaN/Al_(x2)Ga_((1-x2))N/GaN stack, theelectron mobility is reduced, and electron leakage under a high currentdensity can be alleviated. In addition, the electron-collecting layer120 having fewer pairs of the sub-layers would have better latticequality compared to the conventional electron-collecting layer withgreater number of the pairs of the sub-layers.

Referring to FIG. 2, a first embodiment of a light-emitting diode (LED)device according to the disclosure includes a substrate 200, a bufferlayer 300 disposed on the substrate 200, an N-type cladding layer 400disposed on the buffer layer 300, the aforesaid multi-quantum wellstructure 100 disposed on the N-type cladding layer 400, a P-typecladding layer 600 disposed on the multi-quantum well structure 100, anda P-type contact layer 700 disposed on the P-type cladding layer 600.The LED device also includes an electron-blocking layer 500 disposedbetween the multi-quantum well structure 100 and the P-type claddinglayer 600. The electron-blocking layer 500 has aAl_(x3)In_(y3)Ga_((1-x3-y3))N layer or aAl_(x3)In_(y3)Ga_((1-x3-y3))/Al_(x4)In_(y4)Ga_((1-x4-y4))N superlatticestructure, where 0≤x3≤1, 0≤y3≤1, 0≤x4≤1, 0≤y4≤1, x3 and x4 cannot bothbe 1 or 0, y3 and y4 cannot both be 1 or 0, x3 and y3 cannot both be 0,and x4 and y4 cannot both be 0. In this embodiment, theelectron-blocking layer 500 has a thickness ranging from 200 Å to 300 Å.

In comparison to a conventional multi-quantum well structure having aGaN potential barrier sub-layer, the potential barrier sub-layer(s) ofthe electron-collecting layer 120 having the GaN/Al_(x2)Ga_((1-x2))N/GaNstack and the potential barrier sub-layer(s) of the active layer 130having the GaN/Al_(x1)In_(y1)Ga_((1-x1-y1))N stack have higher bandgaps. Therefore, the electron-collecting layer 120 and the active layer130 would cooperate with the electron-blocking layer 500 to scatter andblock electrons. In addition, as compared to the conventionalelectron-blocking layer, the electron-blocking layer 500 of thedisclosure has a smaller thickness, e.g., 200 Å to 300 Å, whichalleviates the light-blocking effect caused by a greater thickness ofthe conventional electron-blocking layer and improves the brightness ofthe LED device.

Further, since the one of the potential barrier sub-layers of the firstactive layer unit 131 having the GaN/Al_(x1)In_(y1)Ga_((1-x1-y1))N stackis disposed farthest away from the electron-collecting layer 120 (i.e.,immediately adjacent to the electron-blocking layer 500), the potentialbarrier sub-layer having the GaN/Al_(x1)In_(y1)Ga_((1-x1-y1))N stack maycapture electrons leaking from the multi-quantum well structure 100.Moreover, the potential barrier sub-layer having theGaN/Al_(x1)In_(y1)Ga_((1-x1-y1))N stack may improve the lattice qualityat an interface between the stress relief layer 110 and theelectron-collecting layer 120 and an interface between theelectron-collecting layer 120 and the active layer 130, and may preventa dopant of the P-type cladding layer 600 from permeating into theactive layer 130 during formation of the P-type cladding layer 600.

Second Embodiment

Referring to FIG. 3, a second embodiment of the multi-quantum wellstructure 100 according to the disclosure is similar to the firstembodiment of the multi-quantum well 100 except that the secondembodiment of the multi-quantum well structure 100 further includes asecond active layer unit 132 that is disposed on the first active layerunit 131. The second active layer unit 132 includes multiple pairs ofsub-layers, the sub-layers in each pair including a potential barriersub-layer and a potential well sub-layer. The plurality of potentialbarrier sub-layers and the plurality of potential well sub-layers arealternately stacked. Each of the potential barrier sub-layers of thefirst active layer unit 131 has a band gap larger than that of each ofthe potential barrier sub-layers of the second active layer unit 132. Inthis embodiment, each of the potential barrier sub-layers of the secondactive layer unit 132 is a GaN layer.

In certain embodiments, each of the potential barrier sub-layers of thefirst active layer unit 131 has the GaN/Al_(x1)In_(y1)Ga_((1-x1-y1))Nstack.

In certain embodiments, the first active layer unit 131 includes 4 to 8pairs of the sub-layers, while the second active layer unit 132 includes5 to 10 pairs of the sub-layers.

In certain embodiments, in the GaN/Al_(x1)In_(y1)Ga_((1-x1-y1))N stackof the first active layer unit 131, y1=0 and 0.02≤x1≤0.06.

In certain embodiments, the first active layer unit 131 is disposedbetween the second active layer unit 132 and the electron-collectinglayer 120.

By forming the first active layer unit 131, electron leakage problemunder a high current density may be reduced, and the rate of radiativerecombination between electrons and holes and the internal quantumefficiency can be increased, thereby improving the efficiency droopphenomenon. Moreover, the lattice defect in the InGaN potential wellsub-layers of the first active layer unit 131 may also be eliminated.

Referring to FIG. 4, a second embodiment of the LED device is similar tothe first embodiment of the LED device except that the second embodimentof the LED device includes the second embodiment of the multi-quantumwell structure 100 according to the disclosure. In the second embodimentof the LED device, the first active layer unit 131 has 4 to 8 pairs ofthe sub-layers, and the second active layer unit 132 has 5 to 10 pairsof the sub-layers. In addition, the electron-blocking layer 500 in thesecond embodiment of the LED device has a thickness of 250 Å to 300 Å,and has the Al_(x3)In_(y3)Ga_((1-x3-y3))/Al_(x4)In_(y4)Ga_((1-x4-y4))Nsuperlattice structure, where 0.05≤x3≤0.2, 0≤y3≤0.10, 0.05≤x4≤0.2 and0≤y4≤0.10.

Third Embodiment

Referring to FIG. 5, a third embodiment of the multi-quantum wellstructure 100 according to the disclosure includes a stress relief layer110, an electron-collecting layer 120 disposed on the stress relieflayer 110, an interfacial layer 140 disposed on the electron-collectinglayer 120, and an active layer 130 disposed on the interfacial layer 140oppositely of the electron-collecting layer 120. The active layer 130includes a first active layer unit 131 that is disposed on theinterfacial layer 140, and a second active layer unit 132 that isdisposed on the first active layer unit 131 oppositely of theinterfacial layer 140.

The first active layer unit 131 of this embodiment has a structuresimilar to that of the first active layer unit 131 disclosed in thesecond embodiment, except that, in this embodiment, a number of thepairs of the sub-layers in the first active layer unit 131 ranges from 3to 5. It should be noted that each of the potential barrier sub-layersof the first active layer unit 131 may have theGaN/Al_(x1)In_(y1)Ga_((1-x1-y1))N stack. In certain embodiments, in theGaN/Al GaN/Al_(x1)In_(y1)Ga_((1-x1-y1))N stack of the first active layerunit 131, y1=0 and 0.02≤x1≤0.06.

The second active layer unit 132 of this embodiment includes multiplepairs of sub-layers, the sub-layers in each pair including a potentialbarrier sub-layer and a potential well sub-layer.

The plurality of potential barrier sub-layers and the plurality ofpotential well sub-layers are alternately stacked. Each of the potentialbarrier sub-layers of the first active layer unit 131 has a band gaplarger than that of each of the potential barrier sub-layers of thesecond active layer unit 132. In this embodiment, one of the potentialbarrier sub-layers of the second active layer unit 132 (e.g., the onedisposed farthest away from the first active layer unit 131) has aGaN/Al_(x1)Ga_((1-x1))N/GaN stack (0.1≤x1≤1), and has a thicknessranging from 80 Å to 120 Å, and a thickness of Al_(x1)Ga_((1-x1))N inthe GaN/Al_(x1)Ga_((1-x1))N/GaN stack ranges from 20 Å to 30 Å. For theremainder of the potential barrier sub-layers of the second active layerunit 132, each of the potential barrier sub-layers is a GaN layer. Eachof the potential well sub-layers of the second active layer unit 132 isan InGaN layer. In this embodiment, a number of the pairs of thesub-layers in the second active layer unit 131 ranges from 3 to 5.

The electron-collecting layer 120 in this embodiment has the samestructure as the electron-collecting layer 120 disclosed in the firstembodiment. The interfacial layer 140 disposed between theelectron-collecting layer 120 and the active layer 130 has a band gapsmaller than that of each of the potential well sub-layers of the activelayer 130. The interfacial layer 140 may confine movement of theelectrons and can reduce electron mobility. In certain embodiments, theinterfacial layer 140 is an InN layer. In addition, the interfaciallayer 140 may alleviate lattice difference between the active layer 130and the one of the potential barrier sub-layers of theelectron-collecting layer 120 farthest away from the stress relief layer110. Referring to FIG. 6, a third embodiment of the

LED device according to the disclosure is similar to the secondembodiment of the LED device except that the third embodiment of the LEDdevice includes the third embodiment of the multi-quantum well structure100 and that the electron-blocking layer 500 is aAl_(x3)In_(y3)Ga_((1-x3-y3))N layer, where 0.05≤x3≤0.2, 0≤y3≤0.1, andhas a thickness ranging from 220 Å to 280 Å.

In sum, with the GaN/Al_(x1)In_(y1)Ga_((1-x1-y1))N stack of the firstactive layer unit, the GaN/Al_(x1)Ga_((1-x1))N/GaN stack of the secondactive layer unit, and the GaN/Al_(x2)Ga_((1-x2))N/GaN stack of theelectron-collecting layer, each having a band gap larger than that ofGaN, the multi-quantum well structure 100 of the disclosure exhibitsimproved electron-blocking effect, and alleviates the electron leakageand efficiency droop phenomena. Moreover, the thickness of theelectron-blocking layer 500 may be reduced so as to enhance thelight-emitting efficiency of the LED device.

In the description above, for the purposes of explanation, numerousspecific details have been set forth in order to provide a thoroughunderstanding of the embodiments. It will be apparent, however, to oneskilled in the art, that one or more other embodiments may be practicedwithout some of these specific details. It should also be appreciatedthat reference throughout this specification to “one embodiment,” “anembodiment,” an embodiment with an indication of an ordinal number andso forth means that a particular feature, structure, or characteristicmay be included in the practice of the disclosure. It should be furtherappreciated that in the description, various features are sometimesgrouped together in a single embodiment, figure, or description thereoffor the purpose of streamlining the disclosure and aiding in theunderstanding of various inventive aspects, and that one or morefeatures or specific details from one embodiment may be practicedtogether with one or more features or specific details from anotherembodiment, where appropriate, in the practice of the disclosure.

While the disclosure has been described in connection with what areconsidered the exemplary embodiments, it is understood that thisdisclosure is not limited to the disclosed embodiments but is intendedto cover various arrangements included within the spirit and scope ofthe broadest interpretation so as to encompass all such modificationsand equivalent arrangements.

What is claimed is:
 1. A multi-quantum well structure comprising: astress relief layer; an electron-collecting layer disposed on saidstress relief layer; and an active layer including a first active layerunit that is disposed on said electron-collecting layer and thatincludes a plurality of potential barrier sub-layers and a plurality ofpotential well sub-layers being alternately stacked; wherein at leastone of said potential barrier sub-layers of said first active layer unithas a GaN/Al_(x1)In_(y1)Ga_((1-x1-y1))N stack, where 0≤x1≤1 and 0≤y1<1,said one of said potential barrier sub-layers having saidGaN/Al_(x1)In_(y1)Ga_((1-x1-y1))N stack is disposed farthest away fromsaid electron-collecting layer, and said one of said potential barriersub-layers of said first active layer unit farthest away from saidelectron-collecting layer is undoped, and for the remainder of saidpotential barrier sub-layers of said first active layer unit, each ofsaid potential barrier sub-layers is one of a n-doped layer and ap-doped layer.
 2. The multi-quantum well structure as claimed in claim1, wherein in said GaN/Al_(x1)In_(y1)Ga_((1-x1-y1))N stack, y1=0 and0.05≤x1≤1.
 3. The multi-quantum well structure as claimed in claim 1,wherein said one of said potential barrier sub-layers of said firstactive layer unit farthest away from said electron-collecting layer hasa thickness ranging from 140 Å to 190 Å, and thickness ofGaN/Al_(x1)In_(y1)Ga_((1-x1-y1))N in theGaN/Al_(x1)In_(y1)Ga_((1-x1-y1))N stack ranges from 20 Å to 30 Å.
 4. Themulti-quantum well structure as claimed in claim 1, wherein: said activelayer further includes a second active layer unit that is disposed onsaid first active layer unit and that includes a plurality of potentialbarrier sub-layers and a plurality of potential well sub-layers beingalternately stacked; and each of said potential barrier sub-layers ofsaid first active layer unit has a band gap larger than that of each ofsaid potential barrier sub-layers of said second active layer unit. 5.The multi-quantum well structure as claimed in claim 4, wherein each ofsaid potential barrier sub-layers of said second active layer unit is aGaN layer.
 6. The multi-quantum well structure as claimed in claim 5,wherein in said GaN/Al_(x1)In_(y1)Ga_((1-x1-y1))N stack, y1=0 and0.02≤x1≤0.06.
 7. The multi-quantum well structure as claimed in claim 4wherein said first active layer unit is disposed between said secondactive layer unit and said electron-collecting layer.
 8. Themulti-quantum well structure as claimed in claim 4, wherein at least oneof said potential barrier sub-layers of said second active layer unithas a GaN/Al_(x1)Ga_((1-x1))N/GaN stack, where 0≤x1≤1, and for theremainder of said potential barrier sub-layers of said second activelayer unit, each of said potential barrier sub-layers is a GaN layer. 9.The multi-quantum well structure as claimed in claim 1, furthercomprising an interfacial layer that is disposed between saidelectron-collecting layer and said active layer and that has a band gapsmaller than that of each of said potential well sub-layers of saidfirst active layer unit.
 10. The multi-quantum well structure as claimedin claim 1, wherein: said electron-collecting layer includes a pluralityof potential barrier sub-layers and a plurality of potential wellsub-layers that are alternately stacked; one of said potential barriersub-layers of said electron-collecting layer farthest away from saidstress relief layer has a GaN/Al_(x2)Ga_((1-x2))N/GaN stack, where0≤x2≤1, and for the remainder of said potential barrier sub-layers ofsaid electron-collecting layer, each of said potential barriersub-layers is a GaN layer; and each of said potential well sub-layers ofsaid electron-collecting layer is a InGaN layer.
 11. An LED devicecomprising: a substrate; a buffer layer disposed on said substrate; aN-type cladding layer disposed on said buffer layer; a multi-quantumwell structure as claimed in claim 1, which is disposed on said N-typelayer; a P-type cladding layer disposed on said multi-quantum wellstructure; and a P-type contact layer disposed on said P-type layer. 12.The LED device as claimed in claim 11, further comprising anelectron-blocking layer disposed between said multi-quantum wellstructure and said P-type cladding layer.
 13. The LED device as claimedin claim 12, wherein said electron-blocking layer has a thicknessranging from 200 Å to 300 Å.
 14. The LED device as claimed in claim 12,wherein said electron-blocking layer has one of aAl_(x3)In_(y3)Ga_((1-x3-y3))N layer and aAl_(x3)In_(y3)Ga_((1-x3-y3))/Al_(x4)In_(y4)Ga_((1-x4-y4))N superlatticelayer, where 0≤x3≤1, 0≤y3≤1, 0≤x4≤1 and 0≤y4≤1, x3 and x4 cannot both be1 or 0, y3 and y4 cannot both be 1 or 0, x3 and y3 cannot both be 0, andx4 and y4 cannot both be
 0. 15. The LED device as claimed in claim 11,wherein: said active layer further includes a second active layer unitthat is disposed on said first active layer unit and that includes aplurality of potential barrier sub-layers and a plurality of potentialwell sub-layers being alternately stacked; and each of said potentialbarrier sub-layers of said first active layer unit has a band gap largerthan that of each of said potential barrier sub-layers of said secondactive layer unit.
 16. The LED device as claimed in claim 15, whereineach of said potential barrier sub-layers of said second active layerunit is a GaN layer.
 17. The LED device as claimed in claim 15, whereinat least one of said potential barrier sub-layers of said second activelayer unit has a GaN/Al_(x1)Ga_((1-x1))N/GaN stack, where 0<x1≤1, andfor the remainder of said potential barrier sub-layers of said secondactive layer unit, each of said potential barrier sub-layers is a GaNlayer.
 18. The LED device as claimed in claim 11, wherein: saidelectron-collecting layer includes a plurality of potential barriersub-layers and a plurality of potential well sub-layers that arealternately stacked; one of said potential barrier sub-layers of saidelectron-collecting layer farthest away from said stress relief layerhas a GaN/Al_(x2)Ga_((1-x2))N/GaN stack, where 0≤x2≤1, and for theremainder of said potential barrier sub-layers of saidelectron-collecting layer, each of said potential barrier sub-layers isa GaN layer; and each of said potential well sub-layers of saidelectron-collecting layer is an InGaN layer.